An high-pressure liquid chromatographic method was used to measure allopurinol and oxipurinol in plasma and urine in 6 healthy volunteers after a single intravenous or oral dose of allopurinol. The influence of coadministered benzbromarone and hydrochlorothiazide on the pharmacokinetics of allopurinol and oxipurinol was also investigated. After intravenous injection of allopurinol 300 mg the plasma disappearance was biexponential, with a mean distribution half-life of 2.32 +/- 1.08 min (mean +/- SD) and an elimination half-life of 47.8 +/- 10.6 min. The total clearance of allopurinol was 11.37 +/- 2.70 ml/min/kg, whereas its renal clearance was only 1.73 +/- 0.79 ml/min/kg. Oxipurinol disappeared monoexponentially from plasma with a mean half-life of 12.2 +/- 2.6 h. Its renal clearance was 0.42 +/- 0.091 ml/min/kg. After oral administration of allopurinol 300 mg the peak plasma concentration of 2.1 +/- 0.6 micrograms/ml (1.5 x 10(-5) M) was reached within 30 to 120 min. The peak level of oxipurinol of 5.8 +/- 1.5 micrograms/ml (3.8 x 10(-5) M) was found within 2 to 5 h after intravenous and oral allopurinol. The bioavailability of oral allopurinol computed from plasma data was 90.4 +/- 8.7%. The total recovery from urine was 77% (allopurinol 8%, oxipurinol 69%) after oral and 88% after i.v. administration. It was concluded that about 10% of the oral dose was not absorbed and that 12% was eliminated by an unknown mechanism, presumably as riboside. The pharmacokinetics of allopurinol and oxipurinol were not significantly influenced by coadministration of benzbromarone or hydrochlorothiazide.